1. Field of the Invention
This invention relates to forming apparatus operating at high pressure and, especially, to hydraulic presses for compressing pulverulent materials or the like.
2. Prior Art
Presses used to compress ceramic powders into predetermined shapes have conventionally involved friction-driven screw rams such as shown in U.S. Pat. No. 1,503,619 to Zeh or 1,790,041 to Crossley. U.S. Pat. No. 3,604,076 to Leonard Brown, et al. is a later form of this type of machine in which the ram-upper die combination is hydraulically raised and lowered. In it an independent friction-driven, screw-operated mechanism performs the preliminary "de-airing" step (optional) as well as exerting high pressure compression on the floating ram-die assembly as it rests on the pulverulent material.
The hybrid mechanism of the Brown, et al patent referred to above employed hydraulic piston rods passed through flanged portions of the upper die assembly, with a set of lower nuts screwed on the rods below the die assembly and a set of upper nuts screwed to the ends of the rods above the die assembly. As the upper die entered the mold cavity, the die assembly rested upon and was supported by the lower set of nuts. When the upper die rested upon the powder solely by its weight, the flanges on the ram were above, not in contact with, the set of lower nuts. When the friction-driven pressure hammer was lowered to force the upper die assembly downward with high pressure against the powder, the flanges of the ram were forced downward again into contact with the upper surface of the lower nuts. Switches on the ram cooperating with switch elements on a side vertical member signalled the control console to energize the friction disc which rotated the pressure screw to produce the hammering of the die assembly for the de-airing or final forming operations. Normally, the upper set of nuts were not used in either of these operations.
U.S. Pat. No. 3,225,410 to Boyer shows a wholly-hydraulically operated press wherein there is a ram from which, in a lost-motion relation, an upper die subassembly is suspended. That press has piston rods to which the ram is fixedly attached to lower the ram-upper die combination at a rapid speed into contact with the powder to be compressed. Then a hydraulically-operated hammer is made to produce repeated high pressure impacts downwardly on the upper die subassembly to de-air and/or produce the final compression of the powder to be formed.
The prior art left something to be desired insofar as its cyclic rate was concerned as well as its simplicity and reliability of operation.
It is therefore among the objects of the present invention to provide a hydraulic press with a considerably improved cyclic rate of operation and which employs a fast, simple and reliable mechanism.